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<div class="title">samples/cpp/tutorial_code/ml/introduction_to_pca/introduction_to_pca.cpp</div>  </div>
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<p>Check <a class="el" href="../../d1/dee/tutorial_introduction_to_pca.html">the corresponding tutorial</a> for more details</p>
<div class="fragment"><div class="line"></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d0/d9c/core_2include_2opencv2_2core_8hpp.html">opencv2/core.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d1/d4f/imgproc_2include_2opencv2_2imgproc_8hpp.html">opencv2/imgproc.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &quot;<a class="code" href="../../d4/dd5/highgui_8hpp.html">opencv2/highgui.hpp</a>&quot;</span></div><div class="line"><span class="preprocessor">#include &lt;iostream&gt;</span></div><div class="line"></div><div class="line"><span class="keyword">using namespace </span><a class="code" href="../../d8/dcc/namespacestd.html">std</a>;</div><div class="line"><span class="keyword">using namespace </span><a class="code" href="../../d2/d75/namespacecv.html">cv</a>;</div><div class="line"></div><div class="line"><span class="comment">// Function declarations</span></div><div class="line"><span class="keywordtype">void</span> <a name="a0"></a><a class="code" href="../../d9/d6a/group__aruco.html#ga16fda651a4e6a8f5747a85cbb6b400a2">drawAxis</a>(<a name="_a1"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a>&amp;, <a name="_a2"></a><a class="code" href="../../db/d4e/classcv_1_1Point__.html">Point</a>, <a class="code" href="../../db/d4e/classcv_1_1Point__.html">Point</a>, <a name="_a3"></a><a class="code" href="../../d1/da0/classcv_1_1Scalar__.html">Scalar</a>, <span class="keyword">const</span> <span class="keywordtype">float</span>);</div><div class="line"><span class="keywordtype">double</span> getOrientation(<span class="keyword">const</span> vector&lt;Point&gt; &amp;, <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a>&amp;);</div><div class="line"></div><div class="line"><span class="keywordtype">void</span> <a class="code" href="../../d9/d6a/group__aruco.html#ga16fda651a4e6a8f5747a85cbb6b400a2">drawAxis</a>(<a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a>&amp; img, <a class="code" href="../../db/d4e/classcv_1_1Point__.html">Point</a> p, <a class="code" href="../../db/d4e/classcv_1_1Point__.html">Point</a> q, <a class="code" href="../../d1/da0/classcv_1_1Scalar__.html">Scalar</a> colour, <span class="keyword">const</span> <span class="keywordtype">float</span> <a name="a4"></a><a class="code" href="../../d6/d84/namespacecv_1_1quality_1_1quality__utils.html#ae55d1c89ff5761730174745401162743">scale</a> = 0.2)</div><div class="line">{</div><div class="line">    <span class="keywordtype">double</span> angle = <a name="a5"></a><a class="code" href="../../df/dfc/group__cudev.html#ga1096ba687de70142e095cc791a8bcd65">atan2</a>( (<span class="keywordtype">double</span>) p.<a name="a6"></a><a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a> - q.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a>, (<span class="keywordtype">double</span>) p.<a name="a7"></a><a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a> - q.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a> ); <span class="comment">// angle in radians</span></div><div class="line">    <span class="keywordtype">double</span> hypotenuse = <a name="a8"></a><a class="code" href="../../d0/de1/group__core.html#ga9070b6a3f093dd952d973819b06f4906">sqrt</a>( (<span class="keywordtype">double</span>) (p.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a> - q.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a>) * (p.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a> - q.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a>) + (p.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a> - q.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a>) * (p.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a> - q.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a>));</div><div class="line"></div><div class="line">    <span class="comment">// Here we lengthen the arrow by a factor of scale</span></div><div class="line">    q.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a> = (int) (p.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a> - <a class="code" href="../../d6/d84/namespacecv_1_1quality_1_1quality__utils.html#ae55d1c89ff5761730174745401162743">scale</a> * hypotenuse * <a name="a9"></a><a class="code" href="../../d0/de1/group__core.html#gaf0f2fe47183d063fb7415097fbadb570">cos</a>(angle));</div><div class="line">    q.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a> = (int) (p.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a> - <a class="code" href="../../d6/d84/namespacecv_1_1quality_1_1quality__utils.html#ae55d1c89ff5761730174745401162743">scale</a> * hypotenuse * <a name="a10"></a><a class="code" href="../../d0/de1/group__core.html#ga53a8656033a51db64caa72ee9d4e93b4">sin</a>(angle));</div><div class="line">    <a name="a11"></a><a class="code" href="../../d6/d6e/group__imgproc__draw.html#ga7078a9fae8c7e7d13d24dac2520ae4a2">line</a>(img, p, q, colour, 1, <a name="a12"></a><a class="code" href="../../d6/d6e/group__imgproc__draw.html#ggaf076ef45de481ac96e0ab3dc2c29a777a85fdabe5335c9e6656563dfd7c94fb4f">LINE_AA</a>);</div><div class="line"></div><div class="line">    <span class="comment">// create the arrow hooks</span></div><div class="line">    p.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a> = (int) (q.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a> + 9 * <a class="code" href="../../d0/de1/group__core.html#gaf0f2fe47183d063fb7415097fbadb570">cos</a>(angle + <a name="a13"></a><a class="code" href="../../db/de0/group__core__utils.html#ga677b89fae9308b340ddaebf0dba8455f">CV_PI</a> / 4));</div><div class="line">    p.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a> = (int) (q.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a> + 9 * <a class="code" href="../../d0/de1/group__core.html#ga53a8656033a51db64caa72ee9d4e93b4">sin</a>(angle + <a class="code" href="../../db/de0/group__core__utils.html#ga677b89fae9308b340ddaebf0dba8455f">CV_PI</a> / 4));</div><div class="line">    <a class="code" href="../../d6/d6e/group__imgproc__draw.html#ga7078a9fae8c7e7d13d24dac2520ae4a2">line</a>(img, p, q, colour, 1, <a class="code" href="../../d6/d6e/group__imgproc__draw.html#ggaf076ef45de481ac96e0ab3dc2c29a777a85fdabe5335c9e6656563dfd7c94fb4f">LINE_AA</a>);</div><div class="line"></div><div class="line">    p.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a> = (int) (q.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a4c96fa7bdbfe390be5ed356edb274ff3">x</a> + 9 * <a class="code" href="../../d0/de1/group__core.html#gaf0f2fe47183d063fb7415097fbadb570">cos</a>(angle - <a class="code" href="../../db/de0/group__core__utils.html#ga677b89fae9308b340ddaebf0dba8455f">CV_PI</a> / 4));</div><div class="line">    p.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a> = (int) (q.<a class="code" href="../../db/d4e/classcv_1_1Point__.html#a157337197338ff199e5df1a393022f15">y</a> + 9 * <a class="code" href="../../d0/de1/group__core.html#ga53a8656033a51db64caa72ee9d4e93b4">sin</a>(angle - <a class="code" href="../../db/de0/group__core__utils.html#ga677b89fae9308b340ddaebf0dba8455f">CV_PI</a> / 4));</div><div class="line">    <a class="code" href="../../d6/d6e/group__imgproc__draw.html#ga7078a9fae8c7e7d13d24dac2520ae4a2">line</a>(img, p, q, colour, 1, <a class="code" href="../../d6/d6e/group__imgproc__draw.html#ggaf076ef45de481ac96e0ab3dc2c29a777a85fdabe5335c9e6656563dfd7c94fb4f">LINE_AA</a>);</div><div class="line">}</div><div class="line"></div><div class="line"><span class="keywordtype">double</span> getOrientation(<span class="keyword">const</span> vector&lt;Point&gt; &amp;pts, <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> &amp;img)</div><div class="line">{</div><div class="line">    <span class="comment">//Construct a buffer used by the pca analysis</span></div><div class="line">    <span class="keywordtype">int</span> sz = <span class="keyword">static_cast&lt;</span><span class="keywordtype">int</span><span class="keyword">&gt;</span>(pts.size());</div><div class="line">    <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> data_pts = <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a>(sz, 2, <a name="a14"></a><a class="code" href="../../d1/d1b/group__core__hal__interface.html#ga30a562691cc5987bc88eb7bb7a8faf2b">CV_64F</a>);</div><div class="line">    <span class="keywordflow">for</span> (<span class="keywordtype">int</span> i = 0; i &lt; data_pts.<a name="a15"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#abed816466c45234254d25bc59c31245e">rows</a>; i++)</div><div class="line">    {</div><div class="line">        data_pts.<a name="a16"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa5d20fc86d41d59e4d71ae93daee9726">at</a>&lt;<span class="keywordtype">double</span>&gt;(i, 0) = pts[i].x;</div><div class="line">        data_pts.<a class="code" href="../../d3/d63/classcv_1_1Mat.html#aa5d20fc86d41d59e4d71ae93daee9726">at</a>&lt;<span class="keywordtype">double</span>&gt;(i, 1) = pts[i].y;</div><div class="line">    }</div><div class="line"></div><div class="line">    <span class="comment">//Perform PCA analysis</span></div><div class="line">    <a name="_a17"></a><a class="code" href="../../d3/d8d/classcv_1_1PCA.html">PCA</a> pca_analysis(data_pts, <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a>(), PCA::DATA_AS_ROW);</div><div class="line"></div><div class="line">    <span class="comment">//Store the center of the object</span></div><div class="line">    <a class="code" href="../../db/d4e/classcv_1_1Point__.html">Point</a> cntr = <a name="a18"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga1e83eafb2d26b3c93f09e8338bcab192">Point</a>(static_cast&lt;int&gt;(pca_analysis.mean.at&lt;<span class="keywordtype">double</span>&gt;(0, 0)),</div><div class="line">                      static_cast&lt;int&gt;(pca_analysis.mean.at&lt;<span class="keywordtype">double</span>&gt;(0, 1)));</div><div class="line"></div><div class="line">    <span class="comment">//Store the eigenvalues and eigenvectors</span></div><div class="line">    vector&lt;Point2d&gt; eigen_vecs(2);</div><div class="line">    vector&lt;double&gt; eigen_val(2);</div><div class="line">    <span class="keywordflow">for</span> (<span class="keywordtype">int</span> i = 0; i &lt; 2; i++)</div><div class="line">    {</div><div class="line">        eigen_vecs[i] = <a name="a19"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga32986d8c6fd05949688352abd112509f">Point2d</a>(pca_analysis.eigenvectors.at&lt;<span class="keywordtype">double</span>&gt;(i, 0),</div><div class="line">                                pca_analysis.eigenvectors.at&lt;<span class="keywordtype">double</span>&gt;(i, 1));</div><div class="line"></div><div class="line">        eigen_val[i] = pca_analysis.eigenvalues.at&lt;<span class="keywordtype">double</span>&gt;(i);</div><div class="line">    }</div><div class="line"></div><div class="line">    <span class="comment">// Draw the principal components</span></div><div class="line">    <a name="a20"></a><a class="code" href="../../d9/db7/group__datasets__gr.html#gga610754124ced68d1f05760b5948fbb76a6f0d8b2d9e3e947b2a5c1eff9e81ee95">circle</a>(img, cntr, 3, <a name="a21"></a><a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(255, 0, 255), 2);</div><div class="line">    <a class="code" href="../../db/d4e/classcv_1_1Point__.html">Point</a> p1 = cntr + 0.02 * <a class="code" href="../../dc/d84/group__core__basic.html#ga1e83eafb2d26b3c93f09e8338bcab192">Point</a>(static_cast&lt;int&gt;(eigen_vecs[0].x * eigen_val[0]), static_cast&lt;int&gt;(eigen_vecs[0].y * eigen_val[0]));</div><div class="line">    <a class="code" href="../../db/d4e/classcv_1_1Point__.html">Point</a> p2 = cntr - 0.02 * <a class="code" href="../../dc/d84/group__core__basic.html#ga1e83eafb2d26b3c93f09e8338bcab192">Point</a>(static_cast&lt;int&gt;(eigen_vecs[1].x * eigen_val[1]), static_cast&lt;int&gt;(eigen_vecs[1].y * eigen_val[1]));</div><div class="line">    <a class="code" href="../../d9/d6a/group__aruco.html#ga16fda651a4e6a8f5747a85cbb6b400a2">drawAxis</a>(img, cntr, p1, <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(0, 255, 0), 1);</div><div class="line">    <a class="code" href="../../d9/d6a/group__aruco.html#ga16fda651a4e6a8f5747a85cbb6b400a2">drawAxis</a>(img, cntr, p2, <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(255, 255, 0), 5);</div><div class="line"></div><div class="line">    <span class="keywordtype">double</span> angle = <a class="code" href="../../df/dfc/group__cudev.html#ga1096ba687de70142e095cc791a8bcd65">atan2</a>(eigen_vecs[0].y, eigen_vecs[0].x); <span class="comment">// orientation in radians</span></div><div class="line"><span class="comment"></span></div><div class="line">    <span class="keywordflow">return</span> angle;</div><div class="line">}</div><div class="line"></div><div class="line"><span class="keywordtype">int</span> main(<span class="keywordtype">int</span> argc, <span class="keywordtype">char</span>** argv)</div><div class="line">{</div><div class="line">    <span class="comment">// Load image</span></div><div class="line">    <a name="_a22"></a><a class="code" href="../../d0/d2e/classcv_1_1CommandLineParser.html">CommandLineParser</a> parser(argc, argv, <span class="stringliteral">&quot;{@input | pca_test1.jpg | input image}&quot;</span>);</div><div class="line">    parser.about( <span class="stringliteral">&quot;This program demonstrates how to use OpenCV PCA to extract the orientation of an object.\n&quot;</span> );</div><div class="line">    parser.printMessage();</div><div class="line"></div><div class="line">    <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> src = <a name="a23"></a><a class="code" href="../../d4/da8/group__imgcodecs.html#ga288b8b3da0892bd651fce07b3bbd3a56">imread</a>( <a name="a24"></a><a class="code" href="../../d6/dba/group__core__utils__samples.html#ga3a33b00033b46c698ff6340d95569c13">samples::findFile</a>( parser.get&lt;<a class="code" href="../../dc/d84/group__core__basic.html#ga1f6634802eeadfd7245bc75cf3e216c2">String</a>&gt;(<span class="stringliteral">&quot;@input&quot;</span>) ) );</div><div class="line"></div><div class="line">    <span class="comment">// Check if image is loaded successfully</span></div><div class="line">    <span class="keywordflow">if</span>(src.<a name="a25"></a><a class="code" href="../../d3/d63/classcv_1_1Mat.html#abbec3525a852e77998aba034813fded4">empty</a>())</div><div class="line">    {</div><div class="line">        cout &lt;&lt; <span class="stringliteral">&quot;Problem loading image!!!&quot;</span> &lt;&lt; endl;</div><div class="line">        <span class="keywordflow">return</span> EXIT_FAILURE;</div><div class="line">    }</div><div class="line"></div><div class="line">    <a name="a26"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>(<span class="stringliteral">&quot;src&quot;</span>, src);</div><div class="line"></div><div class="line">    <span class="comment">// Convert image to grayscale</span></div><div class="line">    <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> gray;</div><div class="line">    <a name="a27"></a><a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#ga397ae87e1288a81d2363b61574eb8cab">cvtColor</a>(src, gray, <a name="a28"></a><a class="code" href="../../d8/d01/group__imgproc__color__conversions.html#gga4e0972be5de079fed4e3a10e24ef5ef0a353a4b8db9040165db4dacb5bcefb6ea">COLOR_BGR2GRAY</a>);</div><div class="line"></div><div class="line">    <span class="comment">// Convert image to binary</span></div><div class="line">    <a class="code" href="../../d3/d63/classcv_1_1Mat.html">Mat</a> bw;</div><div class="line">    <a name="a29"></a><a class="code" href="../../d7/d1b/group__imgproc__misc.html#gae8a4a146d1ca78c626a53577199e9c57">threshold</a>(gray, bw, 50, 255, <a name="a30"></a><a class="code" href="../../d7/d1b/group__imgproc__misc.html#ggaa9e58d2860d4afa658ef70a9b1115576a147222a96556ebc1d948b372bcd7ac59">THRESH_BINARY</a> | <a name="a31"></a><a class="code" href="../../d7/d1b/group__imgproc__misc.html#ggaa9e58d2860d4afa658ef70a9b1115576a95251923e8e22f368ffa86ba8bce87ff">THRESH_OTSU</a>);</div><div class="line"></div><div class="line">    <span class="comment">// Find all the contours in the thresholded image</span></div><div class="line">    vector&lt;vector&lt;Point&gt; &gt; contours;</div><div class="line">    <a name="a32"></a><a class="code" href="../../d3/dc0/group__imgproc__shape.html#gadf1ad6a0b82947fa1fe3c3d497f260e0">findContours</a>(bw, contours, <a name="a33"></a><a class="code" href="../../d3/dc0/group__imgproc__shape.html#gga819779b9857cc2f8601e6526a3a5bc71a48b9c2cb1056f775ae50bb68288b875e">RETR_LIST</a>, <a name="a34"></a><a class="code" href="../../d3/dc0/group__imgproc__shape.html#gga4303f45752694956374734a03c54d5ffaf7d9a3582d021d5dadcb0e37201a62f8">CHAIN_APPROX_NONE</a>);</div><div class="line"></div><div class="line">    <span class="keywordflow">for</span> (<span class="keywordtype">size_t</span> i = 0; i &lt; contours.size(); i++)</div><div class="line">    {</div><div class="line">        <span class="comment">// Calculate the area of each contour</span></div><div class="line">        <span class="keywordtype">double</span> area = <a name="a35"></a><a class="code" href="../../d3/dc0/group__imgproc__shape.html#ga2c759ed9f497d4a618048a2f56dc97f1">contourArea</a>(contours[i]);</div><div class="line">        <span class="comment">// Ignore contours that are too small or too large</span></div><div class="line">        <span class="keywordflow">if</span> (area &lt; 1e2 || 1e5 &lt; area) <span class="keywordflow">continue</span>;</div><div class="line"></div><div class="line">        <span class="comment">// Draw each contour only for visualisation purposes</span></div><div class="line">        <a name="a36"></a><a class="code" href="../../d6/d6e/group__imgproc__draw.html#ga746c0625f1781f1ffc9056259103edbc">drawContours</a>(src, contours, static_cast&lt;int&gt;(i), <a class="code" href="../../dc/d84/group__core__basic.html#ga599fe92e910c027be274233eccad7beb">Scalar</a>(0, 0, 255), 2);</div><div class="line">        <span class="comment">// Find the orientation of each shape</span></div><div class="line">        getOrientation(contours[i], src);</div><div class="line">    }</div><div class="line"></div><div class="line">    <a class="code" href="../../d7/dfc/group__highgui.html#ga453d42fe4cb60e5723281a89973ee563">imshow</a>(<span class="stringliteral">&quot;output&quot;</span>, src);</div><div class="line"></div><div class="line">    <a name="a37"></a><a class="code" href="../../d7/dfc/group__highgui.html#ga5628525ad33f52eab17feebcfba38bd7">waitKey</a>();</div><div class="line">    <span class="keywordflow">return</span> EXIT_SUCCESS;</div><div class="line">}</div></div><!-- fragment --> </div><!-- contents -->
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